The invention relates generally to filters, and, more particularly, to a dual operation mode all temperature filter using superconducting resonators.
Radio Frequency (RF) filters have been used with cellular base stations and other telecommunications equipment for some time. Such filters are conventionally used to filter out noise and other unwanted signals. For example, bandpass filters are conventionally used to filter out or block radio frequency signals in all but one or more predefined band(s). By way of another example, notch filters are conventionally used to block signals in a predefined radio frequency band.
The relatively recent advancements in superconducting technology have given rise to a new type of RF filter, namely, the high temperature superconducting (HTSC) filter. HTSC filters contain components which are superconductors at or above the liquid nitrogen temperature of 77K. Such filters provide greatly enhanced performance in terms of both sensitivity (the ability to select signals) and selectability (the ability to distinguish desired signals from undesirable noise and other traffic) as compared to conventional filters. However, since known high temperature superconducting (HTSC) materials are only superconductive at relatively low temperatures (e.g., approximately 90K or lower), and are relatively poor conductors at ambient temperatures, such superconducting filters require accompanying cooling systems to ensure the filters are maintained at the proper temperature during use. As a result, the reliability of traditional superconducting filters has been tied to the reliability of the power source. Specifically, if the power source (e.g., a commercial power distribution system) fails (e.g., a black out, a brown out, etc.) for any substantial length of time, the cooling system would likewise fail and, when the corresponding superconducting filters warm sufficiently to prevent superconducting, so too would the filters.
To prevent systems serviced by such filters from failing during these power outages, additional circuitry in the form of RF bypass circuitry was often needed to switch out the failed filter until a suitably cooled environment was returned. Such bypass circuitry added expense and complexity to known systems.
In accordance with an aspect of the invention, a filter is provided. The filter includes a housing defining at least two cavities, an input port, and an output port. It also includes a first non-superconducting resonator disposed in a first one of the cavities; and a first superconducting, resonator disposed in a second one of the cavities.
Preferably, the superconducting resonator comprises a superconducting material including 8-15% silver by weight.
In some embodiments, the filter is further provided with a second superconducting resonator disposed in a third cavity and a second non-superconducting resonator disposed in a fourth cavity. In such embodiments, the first cavity may optionally define an input cavity and the fourth cavity may optionally define an output cavity.
In accordance with another aspect of the invention, a combination comprising a dual operation mode filter and a conventional filter cascaded with the dual operation mode filter is provided. The dual operation mode filter provides a first level of filtering at temperatures below a threshold temperature and a second level of filtering at temperatures above the threshold temperature. The first level is higher than the second level.
In some embodiments, a low noise amplifier is coupled between the dual operation mode filter and the conventional filter. In other embodiments, an isolator is coupled between the dual operation mode filter and the conventional filter.
In some embodiments, the dual operation mode filter comprises a bandpass filter.
Other features and advantages are inherent in the apparatus claimed and disclosed or will become apparent to those skilled in the art from the following detailed description and its accompanying drawings.